Polariscopes for inspecting relatively transparent objects for defects are well known in the art. For example, U.S. Pat. No. 3,177,761 to Redner discloses a polariscope having simultaneously rotatable waveplates to permit measurement of the relative retardation and azimuth of a specimen without having to remove or replace any of the polarizing elements.
U.S. Pat. No. 3,687,555 to Yamamoto et al. discloses a photoelectric polarization analyzer that introduces a half-wave polarizer plate that is rotated in place of elements of the polarization system.
U.S. Pat. No. 3,434,786 to Flynn et al. discloses a dual-beam polariscope using condenser lenses, polarizers and mirrors to obtain two images of a specimen that are focused by a single lens adjustment.
U.S. Pat. No. 3,811,775 to Abu-Saud discloses a stress determining polariscope using plane polarized, polychromatic light that can be swept back and forth across a transparent object being inspected. The object can also be moved along an axis that is transverse to that along which the light is being swept.
U.S. Pat. No. 4,547,067 to Watanabe discloses a fault polariscope for detecting faults and foreign matter in transparent objects. Diffused light transmitted through an object is imaged through a lens system and converted into an electrical signal by a photoelectric detector and processed.
Other patents that are representative of polariscope systems include U.S. Pat. No's. 2,332,308; 3,031,919; 3,373,652; 3,466,129; 3,495,910; 3,549,259; 3,653,767; 3,873,207; 4,171,908; 4,297,032; 4,309,110; 4,400,062; 4,410,277; 4,684,256; and 4,786,802. Also representative is U.S. Statutory Invention Registration No. H76.
While each of these polariscopes functions with a certain degree of efficiency, none discloses the advantages of the improved polariscope of the present invention as is hereinafter more fully described.